Using Scene-Change Transitions To Output An Alert Indicating A Functional State Of A Back-Up Video-Broadcast System

ABSTRACT

In one aspect, an example method for outputting an alert indicating a functional state of a back-up video-broadcast system involves: a computing device receiving a first video-stream that represents first video-content; the computing device generating a first signature based, at least in part, upon an extent of scene-change transitions included within the first video-content; the computing device receiving a second video-stream that represents second video-content; the computing device generating a second signature based, at least in part, upon an extent of scene-change transitions included within the second video-content; the computing device making a determination that the generated first-signature and the generated second-signature lack a threshold extent of similarity; and responsive to the determination that the generated first-signature and the generated second-signature lack the threshold extent of similarity, the computing device outputting an alert.

RELATED DISCLOSURE

This disclosure is a continuation of U.S. patent application Ser. No. 14/676,319 filed on Apr. 1, 2015.

USAGE AND TERMINOLOGY

Throughout this application, with respect to all reasonable derivatives of such terms, and unless otherwise specified (and/or unless the particular context clearly dictates otherwise), each usage of “a” or “an” means at least one, and each usage of “the” means the at least one.

BACKGROUND

Unless otherwise indicated herein, the materials described in this section are not prior art to the claims in this disclosure and are not admitted to be prior art by inclusion in this section.

A video-broadcast system may be configured to generate and broadcast a video stream to a set of receivers (e.g., set-top boxes) for viewing by end-users. In some instances, two different video-broadcast systems (a primary and a back-up) may be configured to generate the same (or substantially the same) video streams at the same (or substantially the same) time. As such, the primary and back-up systems may generate primary and back-up streams, respectively. With this arrangement, the primary system may broadcast the primary stream to the set of receivers unless and until the primary system becomes inoperative, in which case the back-up system may take over and broadcast the back-up stream to the set of receivers instead.

SUMMARY

In a first aspect, an example method for outputting an alert indicating a functional state of a back-up video-broadcast system involves: a computing device receiving a first video-stream that represents first video-content; the computing device generating a first signature based, at least in part, upon an extent of scene-change transitions included within the first video-content; the computing device receiving a second video-stream that represents second video-content; the computing device generating a second signature based, at least in part, upon an extent of scene-change transitions included within the second video-content; the computing device making a determination that the generated first-signature and the generated second-signature lack a threshold extent of similarity; and responsive to the determination that the generated first-signature and the generated second-signature lack the threshold extent of similarity, the computing device outputting an alert.

In a second aspect, a method for outputting an alert indicating a functional state of a back-up video-broadcast system involves: a computing device receiving a first video-stream that represents first video-content; the computing device generating a first signature based, at least in part, upon an extent of scene-change transitions included within the first video-content; the computing device receiving a second signature based, at least in part, upon an extent of scene-change transitions included within second video-content represented by a second video-stream; the computing device making a determination that the generated first-signature and the received second signature lack a threshold extent of similarity; and responsive to the determination that the generated first-signature and the received second signature lack the threshold extent of similarity, the computing device outputting an alert.

In a third aspect, a non-transitory computer-readable medium has stored thereon program instructions that when executed cause a computing device to perform of a set of acts for outputting an alert indicating a functional state of a back-up video-broadcast system. The set of acts involve: receiving a first video-stream that represents first video-content; generating a first signature based, at least in part, upon an extent of scene-change transitions included within the first video-content; receiving a second signature based, at least in part, upon an extent of scene-change transitions included within second video-content represented by a second video-stream; making a determination that the generated first-signature and the received second signature lack a threshold extent of similarity; and responsive to the determination that the generated first-signature and the received second signature lack the threshold extent of similarity, outputting an alert.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified block diagram illustrating an example system according to the present disclosure.

FIG. 2 is a simplified block diagram illustrating another example system according to the present disclosure.

FIG. 3 is a simplified block diagram illustrating an example computing device according to the present disclosure.

FIG. 4 is a flow chart illustrating an example method according to the present disclosure.

FIG. 5 is a simplified diagram of an example scene-change transition signature according to the present disclosure.

FIG. 6 is a simplified diagram of another example scene-change transition signature according to the present disclosure.

FIG. 7 is a flow chart illustrating another example method according to the present disclosure.

DETAILED DESCRIPTION I. Overview

As indicated above, in some instances, primary and back-up systems may generate primary and back-up video streams, respectively, and in the event that the primary system becomes inoperable, the back-up system may broadcast the back-up stream to take the place of the primary stream. Given this, at any given time, it may be desirable to determine a functional state of the back-up system. In particular, it may be desirable to determine whether the back-up system is in fact generating a back-up stream, thus allowing the back-up system to take over if necessary. In the event that the back-up system is not generating a back-up stream, it may be desired to output an alert so that the issue with the back-up system can be addressed.

One approach for determining a functional state of the back-up system involves a computing device conducting a bit-by-bit comparison of a primary stream and a corresponding purported back-up stream to determine whether the streams are exact copies of each other. After making this comparison, if the device determines that there is a discrepancy between the two streams, the device may output an alert (i.e., to indicate that the back-up system is not functioning properly).

However, in some cases, this approach may not provide useful results. This may be the case where the two streams are not identical, but where they represent respective portions of video content that are perceptually indistinguishable from each other (from the perspective of a typical end-user). Such streams may not be identical for a variety of reasons, such as due to a digital signal processing artifact that is present in one stream, but not in the other. Given this scenario, despite the fact that the back-up system is generating a back-up stream that should be considered to be an acceptable back-up of the primary stream, due to the nature of the bit-by-bit comparison, the device may nonetheless output an alert.

The present disclosure provides an alternative and improved approach for determining a functional state of a back-up system, and for outputting an alert indicating the functional state, and is based, at least in part, on a consideration of an extent of scene-change transitions occurring in video content.

As used herein, the term “scene-change transition” refers to a pair of (typically adjacent) frames of video content that are contained in different recording or “cuts.” For example, consider video content showing two individuals in an interview, but that toggles back and forth between recordings from two cameras (e.g., with each camera facing a different individual). In this video content, each toggle represents a scene-change transition. A scene-change transition may also result from the change of traditionally substantive content to traditionally non-substantive content and vice-versa. For example, consider video content having a show-segment portion, followed by a short (e.g., 1 second) set of black frames that serves as a buffer, followed by a commercial portion. In this case, a scene-change transition may occur between the last frame of the show segment portion and the first frame of the buffer. Likewise, another scene-change transition may occur between the last frame of the buffer and the first frame of the commercial portion. Further, a scene-change transition may result from the change between one type of traditionally non-substantive content and another. For example, a change from a black frame to a colorbar frame would be considered a scene-change transition.

In one aspect, disclosed is a method that involves a computing device receiving a first video-stream and a second video-stream, one being a primary stream, and the other being a corresponding purported back-up stream. The first stream represents first video-content and the second stream represents second video-content.

The method further involves the device generating a first signature based, at least in part, upon an extent of scene-change transitions included within the first video-content, and generating a second signature based, at least in part, upon an extent of scene-change transitions included within the second video-content. Accordingly, the signatures may indicate one or more occurrences within the respective video content where a scene-change transition occurs.

The method further involves the device making a determination that the generated first-signature and the generated second-signature lack a threshold extent of similarity, and, responsive to the determination, the device outputting an alert. As compared to the bit-by-bit comparison approach described above, by generating and comparing signatures based on scene-change transitions of the represented content, the device may more accurately determine whether or not a purported back-up stream is in fact a back-up stream. Indeed, in the case where the first and second streams are not identical, but where they represent respective portions of video content that are perceptually indistinguishable from each other, the portions are likely to have the same (or similar) signatures based on scene-change transitions, and therefore, in accordance with the disclosed technique, the device may appropriately forgo outputting an alert. On the other hand, in the case where the respective portions of video content are perceptually distinguishable from each other, in accordance with the disclosed technique, the device may appropriately output an alert (i.e., to indicate that the back-up system is not functioning properly).

II. Example System

FIG. 1 is a simplified block diagram illustrating an example system 100. The system 100 may include at least two video-broadcast systems, including a first system 102 a and a second system 102 b. One of the first and second systems 102 a, 102 b may serve as a primary system, and other may serve as a back-up system. The system 100 may further include a receiver 104, and a computing device 106.

The first system 102 a may include a generation system 108 a and a distribution system 110 a. The generation system 108 a may be configured for generating a first video-stream 112 a, and may include various components, including for example a video source, a router, a switcher, and/or a broadcast automation system. The generation system 108 a may be connected to the distribution system 110 a, which in turn may be connected to the receiver 104. The distribution system 110 a may be configured for distributing the first stream 112 a to the receiver 104. The distribution system 110 a may include various components such as a terrestrial antenna or a satellite, and may be configured for distributing the first stream 112 a to the receiver 104 in a variety of ways (e.g., over the air transmission). The receiver 104 may take a variety of forms, including for example, a television or a television set-top box.

The second system 102 b may be configured in a same or similar manner to that of the first system 102 a. As such, the second system 102 b may include a generation system 108 b and a distribution system 110 b. The generation system 108 b may be configured for generating a second video-stream 112 b, and may include various components, including for example a media source, a router, a switcher, and/or a broadcast automation system. The generation system 108 b may be connected to the distribution system 110 b, which in turn may be connected to the receiver 104. The distribution system 110 b may be configured for distributing the second stream 112 b to the receiver 104. The distribution system 110 b may include various components such as a terrestrial antenna or a satellite, and may be configured for distributing the second stream 112 b to the receiver 104 in a variety of ways.

While the generation system 108 may generate the first stream 112 a and the generation system 108 b may generate the second stream 112 b at or about the same time, the system 100 may be configured such that only one of the distribution systems 110 a, 110 b distributes its respective generated stream to the receiver 104 at a given time. In practice, provided the first system 102 a is operational, the distribution system 110 a may distribute the first stream 112 a to the receiver 104, unless and until the first system 102 b becomes inoperative, in which case the second system 102 b may take over and the distribution system 110 b may distribute the second stream 112 b to the receiver 104 instead. In this scenario, the first system 102 a may be considered the primary system and the second system 102 b may be considered the back-up system. Likewise, the first stream 112 a may be considered the primary stream, and the second stream 112 b may be considered the back-up stream.

Given the possibility of the second system 102 b taking over for the first system 102 a, at any given time, it may be desirable to determine a functional state of the second system 102 b. In particular, it may be desirable to determine whether the second system 102 b is in fact generating a back-up stream, thus allowing the second system 102 b to take over if necessary. In the event that the second up system 102 b is not generating a back-up stream, it may be desired to generate alert so that the issue with the second system 102 b can be addressed (e.g., by an operator or automatically by another system).

The device 106 may be configured to generate such an alert. The device 106 may be connected to both generation systems 108 b, 108 b. With this arrangement, the device 106 may receive the first stream 112 a and the second stream 112 b, and for each stream, generate a respective signature based, at least in part, upon an extent of scene-change transitions included within content represented by the respective stream. Further, the device 106 may make a determination that the generated signatures lack a threshold extent of similarity, and in response to the determination, the device 106 may output an alert.

In some examples, a video-broadcast system may be integrated with an audio-broadcast system, such that a video stream representing video content may be broadcast together with an audio stream representing corresponding audio content. In some instances, the video stream and the audio stream may be combined into a single media stream.

FIG. 2 is a simplified block diagram illustrating an example system 200. The system 200 may be the same as or similar to the system 100, except that the system 200 includes another computing device 114, and a communication network 116 connecting the device 106 and the device 114, and through which the device 106 and the device 114 may communicate. The device 114 is also connected to the generation system 108 b. The communication network 116 may take a variety of forms. For example, the communication network 116 may be a packet-switched network such as the Internet.

With this arrangement, the device 106 may receive the first stream 112 a, and generate a first signature based, at least in part, upon an extent of scene-change transitions included within content represented by the first stream 112 a. Further, the device 114 may receive the second stream 112 b, and generate a second signature based, at least in part, upon an extent of scene-change transitions included within content represented by the second stream 112 b. The device 114 may transmit the generated second-signature to the device 106, and the device 106 may receive the same. The device 106 may then make a determination that the generated first-signature and the received second signature lack a threshold extent of similarity, and in response to the determination, the device 106 may output an alert.

FIG. 3 is a simplified block diagram illustrating an example computing device 300. The device 300 may represent the device 106 or the device 114, for instance. The device 300 may be configured for performing a variety of functions or acts, such as those described in this disclosure (including the accompanying drawings). The device 300 may include various components, including for example, a processor 302, a communication interface 304, a user interface 306, and a data storage 308. The components of the device 300 may be communicatively connected to each other (or other devices or systems) via a system bus, network, or other connection mechanism 310.

The processor 302 may include a general purpose processor (e.g., a microprocessor) and/or a special purpose processor (e.g., a digital signal processor (DSP)).

The communication interface 304 may be configured to allow the device 300 to communicate with one or more devices (or systems) according to one or more protocols. In one example, the communication interface 304 may be a wired interface, such as an Ethernet interface or a high-definition serial-digital-interface (HD-SDI). As another example, the communication interface 304 may be a wireless interface, such as a cellular or WI-FI interface.

The user interface 306 may facilitate interaction with a user of the device, if applicable. As such, the user interface 306 may include input components such as a keyboard, a keypad, a mouse, a touch-sensitive panel, a microphone, and a camera, and output components such as a display screen (which, for example, may be combined with a touch-sensitive panel), a sound speaker, and a haptic feedback system.

The data storage 308 may include one or more volatile, non-volatile, removable, and/or non-removable storage components, such as magnetic, optical, or flash storage, and may be integrated in whole or in part with the processor 302. Further, the data storage 308 may take the form of a non-transitory computer-readable storage medium, having stored thereon program instructions (e.g., compiled or non-compiled program logic and/or machine code) that, when executed by the processor 302, cause the device 300 to perform one or more functions or acts, such as those described in this disclosure. Such program instructions may define or be part of a discrete software application that can be executed in response to certain inputs received from the user interface 306, for instance. The data storage 308 may also store other types of information or data, such as those types described throughout this disclosure.

III. Example Operations

FIG. 4 is a flow chart illustrating an example method 400. At block 402, the method may involve a computing device receiving a first video-stream that represents first video-content. For instance, this may involve the device 106 receiving the first stream 112 a from the generation system 108 a.

At block 404, the method may involve the computing device generating a first signature based, at least in part, upon an extent of scene-change transitions included within the first video-content. For instance, this may involve the device 106 generating the first signature based, at least in part, upon an extent of scene-change transitions included within video-content of the first stream 112 a. In one example, the device 106 may store data representing the generated first-signature in data storage.

The act of generating the first signature may involve identifying a scene-change transition within the first video-content. This may be accomplished using any technique for identifying scene-change transitions as known in the art. An example technique for identifying a scene-change transition is described in U.S. Pat. No. 8,744,186 entitled “Systems and Methods for Identifying a Scene-Change/Non-Scene-Change Transition Between Frames,” which is hereby incorporated by reference herein in its entirety.

The act of generating the first signature may further involve determining a time associated with the identified scene-change transition. In one example, the device 106 may utilize a time synchronization service (e.g., a global positioning system (GPS) time synchronization service), to determine a time at which playout of the scene-change transition occurs. The time may be represented in a variety of formats, such as by specifying a number of hours, minutes, seconds, and frames (which is commonly represented in HH:MM:SS:FF format).

Depending on the manner in which the first signature is generated, the first signature may represent a time of one or more scene-change transitions. Notably, in the case where the first video-stream does not include any scene-change transitions, the first signature may indicate that no such scene-change transitions are present.

FIG. 5 depicts an example first signature 500 in the form of a table with a column for TIME (in HH:MM:SS:FF format). As shown, the first signature 500 includes an indication of three scene-change transitions (each represented as a row), namely ones occurring at time 04:00:00:00, time 04:00:01:08, and time 04:00:03:02.

At block 406, the method may involve the computing device receiving a second video-stream that represents second video-content. For instance, this may involve the device 106 receiving the second stream 112 b from the generation system 108 b.

At block 408, the method may involve the computing device generating a second signature based, at least in part, upon an extent of scene-change transitions included within the second video-content. For instance, this may involve the device 106 generating the second signature based, at least in part, upon an extent of scene-change transitions included within video-content of the second stream 112 b. In one example, the device 106 may store data representing the generated second-signature in data storage.

The device 106 may generate the second signature in a same or a similar manner as that in which it generates the first signature. FIG. 6 depicts an example second signature 600 again in the form of a table with a column for TIME (in HH:MM:SS:FF format). As shown, the second signature 600 includes an indication of three scene-change transitions (each represented as a row), namely ones occurring at time 04:00:00:00, at time 04:00:11:08, and at time 04:00:23:02.

At block 410, the method may involve the computing device making a determination that the generated first-signature and the generated second-signature lack a threshold extent of similarity. For instance, this may involve the device 106 making a determination that the first signature 500 and the second signature 600 lack a threshold extent of similarity.

The threshold extent of similarity may be based on a variety of factors, such as the existence of one or more transitions, and/or the type or time associated with any such transitions. For instance, the device 106 may make the determination that the generated first-signature and the generated second-signature lack a threshold extent of similarity if there is any type of transition represented in the first signature that is not represented in the second signature.

Additionally or alternatively, the device 106 may make the determination that the generated first-signature and the generated second-signature lack a threshold extent of similarity if there is any type of transition, associated with a first time, represented in the first signature that is not represented in the second signature and associated with a second time within a tolerance period of the first time. As such, in the case where the tolerance period is one second, the device 106 may determine that the first signature 500 and the second signature 600 lack a threshold extent of similarity because the scene-change transition at 04:00:11:08 represented by the first signature 500 is not represented in the second signature 600 within that one minute range. Notably though, in the case where the tolerance period is one and one half seconds, the device 106 may determine that the first signature 500 and the second signature 600 have a threshold extent of similarity because the scene-change transition at 04:00:11:08 represented by the first signature 500 is represented in the second signature 600 at 04:00:12:10, which is within the one and one half second tolerance period.

At block 412, the method may involve responsive to the determination that the generated first-signature and the generated second-signature lack the threshold extent of similarity, the computing device outputting an alert. For instance, this may involve responsive to the determination that the first-signature 500 and the second-signature 600 lack the threshold extent of similarity, the device 106 outputting an alert.

The act of outputting an alert may take a variety of forms. For instance, this may involve the device 106 displaying a message. Alternatively or additionally, this may involve the device 106 transmitting an instruction to another system or device. Such an instruction may cause the system or device to initiate a diagnostic and/or repair process in connection with the second system 102 b.

FIG. 7 is a flow chart illustrating an example method 700. At block 702, the method may involve a computing device receiving a first video-stream that represents first video-content. For instance, this may involve the device 106 receiving the first stream 112 a from the generation system 108 a.

At block 704, the method may involve the computing device generating a first signature based, at least in part, upon an extent of scene-change transitions included within the first video-content. For instance, this may involve the device 106 generating the first signature based, at least in part, upon an extent of scene-change transitions included within video-content of the first stream 112 a.

At block 706, the method may involve the computing device receiving a second signature based, at least in part, upon an extent of scene-change transitions included within second video-content represented by a second video-stream. For instance, this may involve the device 106 receiving from the device 114 via the communication network 116, a second signature based, at least in part, upon an extent of scene-change transitions included within the video content represented by the second stream 112 b.

At block 708, the method may involve the computing device making a determination that the generated first-signature and the received second signature lack a threshold extent of similarity. For instance, this may involve the device 106 making a determination that the first signature 500 and the second signature 600 lack a threshold extent of similarity.

At block 710, the method may involve responsive to the determination that the generated first-signature and the received second signature lack the threshold extent of similarity, the computing device outputting an alert. For instance, this may involve responsive to the determination that the first-signature 500 and the second-signature 600 lack the threshold extent of similarity, the device 106 outputting an alert.

The variations discussed above in connection with the method 400 are also applicable in connection with the example method 700.

IV. Example Variations

While one or more acts have been described as being performed by certain devices, systems, or entities (e.g., the computing device 106), the acts may be performed by any device, system, or entity, such as those described in connection with the first system 100 or the second system 200. Furthermore, the devices and systems need not be discrete entities. Some or all of the devices or systems may be combined in a single device.

In addition, the acts described herein need not be performed in the disclosed order, although in some examples and order may be preferred. Also, not all acts need to be performed to achieve the desired advantages of the disclosed systems, devices, and methods, and therefore not all acts are required. Variations discussed in connection with one example may be applied to all other examples disclosed herein.

While select examples of the present disclosure have been described, alterations and permutations of these examples will be apparent to those of ordinary skill in the art. Other changes, substitutions, and alterations are also possible without departing from the invention on its broader aspects as set forth in the following claims. 

1. A method for outputting an alert indicating a functional state of a back-up video-broadcast system, the method comprising: receiving, by a computing device, a first video-stream that represents first video-content; generating, by the computing device, a first signature based, at least in part, upon an extent of scene-change transitions included within the first video-content; receiving, by the computing device, a second video-stream that represents second video-content; generating, by the computing device, a second signature based, at least in part, upon an extent of scene-change transitions included within the second video-content; making, by the computing device, a determination that the generated first-signature and the generated second-signature lack a threshold extent of similarity; and responsive to the determination that the generated first-signature and the generated second-signature lack the threshold extent of similarity, outputting, by the computing device, an alert.
 2. The method of claim 1, wherein generating the first signature comprises identifying a scene-change transition within the first video-content.
 3. The method of claim 2, wherein generating the first signature comprises determining a playout time of the identified scene-change transition.
 4. The method of claim 1, wherein generating the first signature comprises identifying multiple scene-change transitions within the first video-content.
 5. The method of claim 1, wherein the generated first-signature represents a first transition that is associated with a first time, wherein making the determination that the generated first-signature and the generated second-signature lack a threshold extent of similarity comprises determining that the generated second-signature does not represent a second transition that is associated with a time that is within a tolerance period of the first time.
 6. The method of claim 1, wherein outputting an alert comprises displaying a message.
 7. The method of claim 1, wherein outputting an alert comprises transmitting an instruction.
 8. The method of claim 1, wherein the first video-stream was generated by a primary video-broadcast system, and wherein the second video-stream was generated by the back-up video-broadcast system.
 9. A method for outputting an alert indicating a functional state of a back-up video-broadcast system, the method comprising: receiving, by a computing device, a first video-stream that represents first video-content; generating, by the computing device, a first signature based, at least in part, upon an extent of scene-change transitions included within the first video-content; receiving, by the computing device, a second signature based, at least in part, upon an extent of scene-change transitions included within second video-content represented by a second video-stream; making, by the computing device, a determination that the generated first-signature and the received second signature lack a threshold extent of similarity; and responsive to the determination that the generated first-signature and the received second signature lack the threshold extent of similarity, outputting, by the computing device, an alert.
 10. The method of claim 9, wherein generating the first signature comprises identifying a scene-change transition within the first video-content.
 11. The method of claim 10, wherein generating the first signature comprises determining a playout time of the identified scene-change transition.
 12. The method of claim 9, wherein generating the first signature comprises identifying multiple scene-change transitions within the first video-content.
 13. The method of claim 9, wherein the generated first-signature represents a first transition that is associated with a first time, wherein making the determination that the generated first-signature and the received second-signature lack a threshold extent of similarity comprises determining that the received second-signature does not represent a second transition that is associated with a time that is within a tolerance period of the first time.
 14. The method of claim 9, wherein outputting an alert comprises displaying a message.
 15. The method of claim 9, wherein outputting an alert comprises transmitting an instruction.
 16. The method of claim 9, wherein the first video-stream was generated by one of a primary video-broadcast system and the back-up video-broadcast system, and wherein the second video-stream was generated by another one of the primary video-broadcast system and the back-up video-broadcast system.
 17. A non-transitory computer-readable medium having stored thereon program instructions that when executed cause a computing device to perform a set of acts for outputting an alert indicating a functional state of a back-up video-broadcast system, the set of acts comprising: receiving a first video-stream that represents first video-content; generating a first signature based, at least in part, upon an extent of scene-change transitions included within the first video-content; receiving a second signature based, at least in part, upon an extent of scene-change transitions included within second video-content represented by a second video-stream; making a determination that the generated first-signature and the received second signature lack a threshold extent of similarity; and responsive to the determination that the generated first-signature and the received second signature lack the threshold extent of similarity, outputting an alert.
 18. The non-transitory computer-readable medium of claim 17, wherein generating the first signature comprises identifying a scene-change transition within the first video-content.
 19. The non-transitory computer-readable medium of claim 18, wherein generating the first signature comprises determining a playout time of the identified scene-change transition.
 20. The non-transitory computer-readable medium of claim 17, wherein the generated first-signature represents a first transition that is associated with a first time, wherein making the determination that the generated first-signature and the received second-signature lack a threshold extent of similarity comprises determining that the received second-signature does not represent a second transition that is associated with a time that is within a tolerance period of the first time.
 21. The non-transitory computer-readable medium of claim 17, wherein outputting an alert comprises displaying a message.
 22. The non-transitory computer-readable medium of claim 17, wherein outputting an alert comprises transmitting an instruction.
 23. The non-transitory computer-readable medium of claim 17, wherein the first video-stream was generated by one of a primary video-broadcast system and a back-up video-broadcast system, and wherein the second video-stream was generated by another one of the primary video-broadcast system and the back-up video-broadcast system. 